core: don't warn if we try to remove a querier that is already gone
core: don't warn if we try to remove a querier that is already gone

This might happen if an iface goes away while we are querying.

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=548952

Distrotech/avahi,heftig/avahi-1,lathiat/avahi,Kisensum/xmDNS-avahi,gloryleague/avahi,gloryleague/avahi,gloryleague/avahi,everbase/catta,everbase/catta,heftig/avahi,Distrotech/avahi,Kisensum/xmDNS-avahi,heftig/avahi-1,Kisensum/xmDNS-avahi,heftig/avahi,lathiat/avahi,Kisensum/xmDNS-avahi,catta-x/catta,lathiat/avahi,heftig/avahi,heftig/avahi-1,catta-x/catta,Distrotech/avahi,heftig/avahi,Kisensum/xmDNS-avahi,Kisensum/xmDNS-avahi,heftig/avahi-1,lathiat/avahi,Distrotech/avahi,everbase/catta,lathiat/avahi,heftig/avahi-1,heftig/avahi,Distrotech/avahi,gloryleague/avahi,catta-x/catta,lathiat/avahi,gloryleague/avahi,Distrotech/avahi,heftig/avahi-1,heftig/avahi,gloryleague/avahi